Marine propeller



June 21, 1966 M. J. NOVAK 3,256,939

MARINE PROPELLER Filed Jan. 11, 1965 United States Patent Office Patented June 21, 1966 3,256,939 MARINE PROPELLER Matthew J. Novak, 17212 Longfellow, Hazel Crest, Ill. Filed Jan. 11, 1965, Ser. No. 424,486 1 Claim. (Cl. 170-16053) This invention relates to marine propellers and more particularly to marine propellers having integral damage protection means.

It is an object of the present invention to provide a novel marine propeller which is protected from damage to the propeller body or to the driving motor by striking foreign objects.

It is another object to provide a marine propeller adapted for automatic, repeatable and non-destructive rotational slip of the propeller body with respect to the motor drive under a torque overload, so as to protect the propeller and motor from damage.

It is a further object of the invention to provide a marine propeller which is adapted to cushion the driving motor from the propeller body.

It is a specific object of the invention to provide a novel marine propeller including an irregular bushing adapted to be mounted to a propeller shaft and a resilient sleeve mounted between this bushing and a propeller body, wherein a cushioned drive of the propeller body is provided, and there is provided automatic rotational propeller slip under torque overload conditions protecting the propeller body and driving engine from damage but applying substantial torque even during slip conditions and automatically returning to normal non slip operation upon cessation of the torque overload conditions.

Further objects and advantages of the invention pertain to the particular arrangement and structure Whereby the above-identified objects and other objects of the invention are attained.

The invention both as to its scope and method of operation will be better understood by reference to the following specification and the drawings forming a part thereof, wherein:

FIGURE 1 is a rear view of a marine propeller in accordance with the invention;

FIGURE 2 is a cross-sectional view of the propeller of FIGURE 1 along the line 22 of FIGURE 1;

FIGURE 3 is a cross-sectional view of the propeller of FIGURE 1 along the line 33 of FIGURE 2;

FIGURE 4 is a perspective view of the bushing and the propeller body reinforcing member thereon of the propeller of FIGURE 1; and

FIGURE 5 is a perspective view of the resilient sleeve of the propeller of FIGURE 1.

Referring to the drawings, there is shown in FIGURE 1 an exemplary marine propeller in accordance with the present invention. The propeller 10 includes generally a polygonal surfaced bushing 20, a resilient tubular sleeve 22, and a marine propeller body 12 with a hub portion 14 with a central bore 18 therethrough and radially extending blades 16. Within the bore '18 is mounted the bushing 20, which is adapted to mount to a marine engine, and the sleeve22, which is mounted between and rotationally connects the polygonal surface of the bushing 20 to the propeller body 12. The novel configuration of the propeller 10 provides a cushioned drive of the propeller body and provides for an automatic rotational slip to protect both the propeller and the driving engine from damaging impacts such as occurwhen the propeller strikes a submerged object.

Describing the marine propeller 10 in further detail,

the bushing 20 preferably serves as the sole mounting for the propeller body and has an interior configuration adapted to be mounted to the drive shaft of a marine engine so as to transmit torque from the engine to the propeller body. A hole 24 may be provided radially through the bushing 20 near one end thereof to mount a conventional shear pin (not shown) securing the bushing to the engine drive shaft. The bushing 20 may be constructed of any suitable material, such as aluminum or bronze, which has sufficient rigidity 'and strength to transmit torque from the engine to the propeller body and support and drive the propeller body.

A principal aspect of the bushing 20 for purposes of the invention is the exterior surface configuration thereof. This preferably includes acentral portion 30, having in cross section a regular polygonal surface configuration, extending over the principal length of the bushing, and cylindrical end portions 31 and 33 of a lesser exterior diameter at each side of the central portion 30. One of the cylindrical end portions 31 'or 33 preferably has a shoulder 26 thereon spaced from the central portion 30. This shoulder 26 may be formed by reducing the diameter of one end of the bushing. Preferably the central portion 30 forms a prism of approximately eight planar faces or surfaces 32 with relatively sharp lines of intersection 34 between the adjacent surfaces 32, the prism preferably being regular and circumscribed to a cylinder concentric to the axis of rotation of the bushing. The lines of surface intersections 34 thereby form the extremities of spaced arcuate extensions from the bushings.

Turning to the sleeve 22, this is preferably an evenly thin-'Walled resilient tubular member fitting between the central portion 30 of the bushing 20 and the central bore 18 to provide a cushioned torque transmission path between the bushing and the propeller body 12. 'Preferably it provides the sole rotational connection between the drive shaft of the engine and the propeller body. The sleeve is preferably formed from molded rubber or other suitable relatively high-strength material which has the property of being deformable by compression yet which resiliently resists such deformation with substantial force. Further, it is preferred that the surfaces of the sleeve have a high coefficient of friction.

The sleeve 22 need not be adapted to transmit to the bushing 20 the axial driving thrust produced by the propeller body in its rotation in the water. This thrust may be borne by the shoulder 26 or other suitable axial thrust bearing means.

The cross-sectional configuration of the sleeve is preferably an even thickness tube with regularly polygonal surfaces, having the same interior configuration as the exterior of the bushing 20 at the central region 30. The

'sleeve 22 is preferably adapted to be mounted over the be made from any other suitable or conventional propeller material. The general configuration of the propeller body 12 or the number of blades 16 thereon is not limited in any manner by the invention, providing only that there is preferably provided the bore 18 centrally into the hub 14 within which the bushing 20 and sleeve 22 may be mounted.

and 42.

Where the propeller body 12 is formed of a plastic material, a reinforcing member 28 is preferably provided. The reinforcing member 28 preferably has a configuration corresponding generally to that of the propeller body 12 only of lesser dimensions. Preferably it includes a central hub reinforcing member 38 and a radially extending blade reinforcing member 36 for each propeller blade 16. The hub reinforcing member 38 preferably has a rim 39 slidably encircling the bushing 20 and abutting the shoulder 26 on the bushing. By this arrangement the entire reinforcing member 28 is removably secured in a fixed position with respect to the bushing 20 even before the propeller body 12 is formed.

A preferred manner of construction of the reinforcing member 28 employs a one-piece sheet-metal member which is cut and formed into the above-described configuration. A preferred material is heat treated thin spring sheet steel, which has a high strength yet has flexibility to allow flexing of the propeller blades upon their impact with foreign objects. Also the blade reinforcing material and the blade material itself preferably have sufiicient flexibility to allow the propeller blades to flex somewhat under high driving torque loads so as to change the blade pitch and thereby improve propulsion etficiency.

Considering the mounting of the propeller body 12, the central bore 18 preferablyhas an interior configuration which accurately corresponds to and fits the exterior configuration of the bushing 20 with the sleeve 22 mounted thereon. That is, the central bore 18 preferably surrounds and is in continuous contact with the surfaces of the sleeve 22 over the central portion 30 and the surfaces of the bushing 20 over the cylindrical portions 31 and 33. Around the cylindrical portions 31 an: 33 the relatively rigid material of the propeller body preferably forms rotational bearing regions 40 and 42 providing rotational stability of the propeller body about the bushing 20. That is, the axis of rotation of the propeller body is thereby held coaxial to the axis of rotation of the bushing, and hence coaxial to the engine drive shaft. However, since the surfaces of the bushing 20 and the bore 18 are both preferably smooth and cylindrical in the bearing regions 40 and 42, continuous rotational slip is allowed between the propeller body and the bushing in these regions.

A preferred method of manufacturing the propeller body 12 is by casting or molding to the desired configuration a suitable plastic material such as that described in the patent to Bihlmire, supra. A suitable conventional mold such as the injection type may be employed.

Prior to the plastic molding operation the sleeve 22 may be slipped into position over the central portion 30. The r-im 39 of the reinforcing member 28 may he slipped over the bushing 20 into abutment with the annular shoulder 26. The hub reinforcing member 38 is thereby held substantially spaced from the sleeve 22. The unitary bushing, sleeve and reinforcing member may then be inserted into the mold and the plastic material injected into the mold. The hub portion 14 and blades 16 are preferably molded as a one-piece propeller body unit which completely encloses and adheres to the reinforcing member 28.

The plastic material preferably flows around and continuously contacts, encircles, and permanently locks to the sleeve 22. The sleeve 22 thereby completely occupies a thin and generally annular space equal to its own dimensions between the inner surface of the central bore 18 and the surface of the bushing 20, and is preferably rotationally fixed with respect to the propeller body.

The plastic further preferably flows into continuous and encircling abutment with the bushing 20 at the cylindrical portions 31 and 33 to form the desired smooth cylindrical surfaces of the rotational bearing regions 40 The plastic flowing around the shoulder 26 forms a reduced diameter region below the shoulder and encloses the rim 39 of the reinforcing member.

A principal advantage in the previously described arrangement for slidably mounting the reinforcing member 28 to the bushing prior to the propeller body molding operation is that the blade reinforcing members 36 are thereby held in proper alignment and will not move during the molding operation. Therefor they may maintain their preferred positions centrally disposed inside the finished blades 16. This is important as the propeller blades 16 are normally thin and a slight misalignment or shifting of the blade reinforcing members during the molding operation can result in the blade reinforcing member being so defectively positioned that the propeller 10 is defective.

Considering now the novel operational advantages of the marine propeller 10, as discussed above the propeller body 12 is not rigidly rotationally secured to the bushing 20 but is driven through the resilient sleeve 22. While in normal operation the propeller 10 operates as a conventional marine propeller, there is a novel provision for a protective limited rotational slip between the propeller body and the bushing 20. The protective slip arrangement of the propeller of the invention has superior operational characteristics to mechanical shear pin connections or other prior slip arrangements, and is simple, automatically operative, and non-destructive.

The basic slip operation employs particularly the resilient deformability of the sleeve 22 and the uneven and non-circular surface configuration of the interior abutting central portion of the bushing 20. In normal operation, with the normal torque loads between the propeller body and the bushing, the nature of this surface configuration and the resiliency of the sleeve material (plus the relatively high friction between the surfaces of the bushing and the sleeve) prevent any substantial relative movement, so that the bushing and propeller body are in cushioned but mutual rotational engagement and the propeller is driven by the engine without any rotational slip. When, however, the propeller blades engage foreign objects with a force sufiicient to temporarily or permanently cause excessive torque loads on the propeller body sufficient to damage the propeller or the engine, then the propeller 10 provides a cushioned rotational slip which allows the propeller to slow or halt its rotation with respect to the engine until the torque overload condition ceases. That is, the bushing 20 is forced into rotation with respect to the sleeve 22 rather than applying this excessive torque to the propeller body. This is allowed by the resilience of the sleeve material. However, there is preferably a rigid lateral and axial connection provided by the rotational bearing regions 40 and 42.

During the slip conditions the projecting edges of the surface intersections 34 rotate inside the sleeve 22 to alternately compress and then release the sections of the sleeve 22. A continuous substantially high torque is thereby required to maintain the rotational slip due to the high resiliency forces as well as the frictional forces. Hence a substantial driving torque is applied to the propeller even during slip conditions. This is an additional operating advantage as this driving torque may allow the propeller to extricate itself from the foreign object by the engine operation, yet without danger of reaching a torque overload.

Once the condition causing the torque overload and consequently the slip is removed, the propeller 10 automatically and immediately returns to normal operating conditions, transmitting applied engine power without rotational slip. This is a major advantage over shear pin arrangements or other destructive slip provisions, whichrequire replacement or resetting before the engine can be operated again. Further, there is little wear engendered during slippage and hence the protective slippage drive disconnect may operate numerous times without need for replacement or repair of any components. In'addition, there is no problem of critical adjustment or readjustment to set the torque overload level at which body and into the water are reduced, resulting in a quieter operation. Correspondingly, jolts and vibration in the propeller body due to striking foreign objects, cavitation, etc., are cushioned and partially absorbed by the sleeve 22 and thereby transmitted at a reduced intensity to the engine and mounting.

Where a preferred high strength plastic propeller body material is used, and a resilient high strength reinforcing member 28 is employed thereon, these physical properties coupled with the protection alforded through the automatic protective slip and cushioned drive provide a propeller which has an extremely high shock resistance. In fact the propeller is virtually unbreakable by impact with underwater obstacles-the most common cause of small marine propeller failure.

It is clear that there has been provided herein a novel marine propeller providing improved protection of the propeller and its driving engine, which protection is provided by a simple, reliable, and long-lasting propeller structure. The apparatus described herein is presently considered to be preferred. However it is understood that numerous variations and modifications may be made by those skilled in the art and it is intended to cover in the appended claim all such variations and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

A marine propeller comprising: a shaft unit adapted to mount to and be rotatably driven by a marine engine, a prismatic portion of said shaft unit having in cross section the form of a regular polygon of approximately eight sides, said shaft unit having cylindrical surfaces at opposite ends of said prismatic portion, at least one of said cylindrical surfaces having a shoulder thereon; a bladed propeller body having a hub portion with a central bore therein, said bore having a prismatic portion closely corresponding to and evenly surroundingly spaced from said prismatic portion of said shaft unit, said bore having cylindrical portions closely rotatably engaging said cylindrical surfaces of said shaft unit; a thin tubular unitary sleeve of resilient material in continuous contact with said prismatic portion of said shaft unit and said prismatic portion of said bore and fully occupying the space therebetween, said tubular sleeve providing cushioned rotational engagement between said shaft unit and said propeller body and providing non-destructive rotational slip between said sleeve and said shaft unit for only a predetermined torque overload therebetween; said propeller body being of unitary plastic construction having a unitary reinforcing member therein corresponding generally in configuration to said propeller body, said reinforcing memher having a cylindrical rim portion closely slidably mounted to said shaft unit at one of said cylindrical surfaces abutting said shoulder.

References Cited by the Examiner UNITED STATES PATENTS References Cited by the Applicant UNITED STATES PATENTS 2,473,665 6/ 1949 Van Nort. 2,498,348 2/ 0' Thompson. 3,033,293 5/ 196-2 Bihlmire.

SAMUEL LEVINE, Primary Examiner. E. A. POWELL, JR., Assistant Examiner. 

